1. Field of the Invention:
The present invention relates to a refrigerant evaporator which is constructed by connecting a plurality of heat-exchanging units provided with refrigerant passages therein.
2. Description of Related Art:
A refrigerant evaporator 1 having a refrigerant flow route shown in FIG. 6 is disclosed in U.S. patent application Ser. No. 08/730990. In the evaporator 1, an inlet side heat-exchanging portion X is disposed at an air downstream side, and an outlet side heat-exchanging portion Y is disposed at an air upstream side. An arrow A represents an air-flow direction. The inlet side heat-exchanging portion X communicates with an upper side inlet tank portion 43 and a lower side inlet tank portion 44. The outlet side heat-exchanging portion Y communicates with an upper side outlet tank portion 47 and a lower side outlet tank portion 48. Heat exchange between the refrigerant flowing in the evaporator 1 and the air flowing outside the evaporator 1 is carried out in the heat-exchanging portions X and Y. The lower side inlet tank portion 44 is separated into a first inlet tank portion "a" and a second inlet tank portion "b" by first partition member 51. The upper side outlet tank portion 47 is separated into a first outlet tank portion "c" and a second outlet tank portion "d" by second partition member 52.
In the evaporator 1, as shown in FIG. 7, a tube 2 through which the refrigerant flows is constructed by connecting a pair of metal plates 4 shown in FIG. 3 to face each other. An inside of the tube 2 is partitioned into an air upstream side refrigerant passage 2a and an air downstream side refrigerant passage 2b by a center rib 49.
The refrigerant flows inside the evaporator 1 in accordance with the following route which is shown by bold arrows in FIG. 6; "refrigerant inlet pipe 8a.fwdarw.refrigerant passage 15.fwdarw.first inlet tank portion "a".fwdarw.air downstream side refrigerant passages 2b.fwdarw.upper side inlet tank portion 43.fwdarw.air downstream side refrigerant passages 2b.fwdarw.second inlet tank portion "b".fwdarw.refrigerant passage 13.fwdarw.first outlet tank portion "c".fwdarw.air upstream side refrigerant passages 2a.fwdarw.lower side outlet tank portion 48.fwdarw.air upstream side refrigerant passages 2a.fwdarw.second outlet tank portion "d".fwdarw.refrigerant passage 14.fwdarw.refrigerant outlet pipe 8b". As shown in FIG. 6, the refrigerant inlet pipe 8a and the refrigerant outlet pipe 8b are connected to the right side of the evaporator 1. The refrigerant passages 14 and 15 are formed at the right side of the evaporator 1. The refrigerant passage 13 is formed at the left side of the evaporator 1.
In the inlet side heat-exchanging portion X and the outlet side heat-exchanging portion Y, the refrigerant flows in the same direction. That is, in FIG. 6, at the right side of the partition members 51 and 52 in the heat exchanging portions X and Y, the refrigerant flows upwardly, while at the left side of the partition plates 51 and 52, the refrigerant flows downwardly.
Further, as shown in FIG. 6, the air downstream side heat-exchanging portion X includes first and second heat-exchanging units 1, 2 having refrigerant passages. In a similar way, the air upstream side heat-exchanging portion Y includes third and fourth heat-exchanging units 3, 4. The refrigerant flows in the heat-exchanging portions X, Y while meandering. Thereby, the evaporation amount of the refrigerant is increased and the cooling ability of the evaporator is improved.
However, when a refrigerating cycle with the above-described evaporator starts under the condition that the cooling load is low, such as in winter, the liquid refrigerant may not return to a compressor enough to lubricate the compressor sufficiently right after the start of the refrigerating cycle.
That is, under the condition that the cooling load is low for example, in winter, the opening degree of an expansion valve (pressure reducing means) becomes small even right after the refrigerating cycle starts, thereby decreasing the refrigerant flow amount. Further, because of the improved cooling ability in the heat-exchanging portions X, Y, most of the liquid refrigerant evaporates and becomes the gas phase refrigerant before reaching the refrigerant outlet pipe 8b.
Therefore, when the refrigerating cycle starts under the above-described condition, it takes a long period until the liquid refrigerant is stored in the evaporator. Thus, after the refrigerating cycle starts, it takes a long period until the liquid refrigerant returns to the compressor. Thereby, lack of the lubricant oil which returns to the compressor with the liquid refrigerant occurs.
Especially, in the refrigerating cycle to which a variable capacity type compressor is applied, when the compressor is controlled to operate a small capacity operation for reducing a starting shock thereof, the refrigerant flow amount is further decreased under the condition that the cooling load is low in winter. Thus, the compressor is less lubricated than that in the above-described normal type refrigerating cycle.